This invention relates to a endoscope for use in, for example, endoscopic urological surgery, and in particular to a resectoscope for use with an electrosurgical instrument.
In International Patent Applications Nos. WO 97/00647, WO 97/24994, WO 97/24993, WO 97/00646, WO 97/48345 and WO 97/48346, the applicants disclose a number of bipolar electrode assemblies for mounting on the distal end of an elongate tubular instrument shaft. In each case, the electrode assembly is designed for operation whilst immersed in a conductive liquid, typically normal saline, through which current flows from a tissue treatment electrode placed on, or adjacent to, tissue to be treated, to a return electrode which is spaced back from the tissue treatment electrode away from the tissue surface. An electrosurgical generator suitable for supplying power to the disclosed electrode assemblies is described and shown in the applicants' European Patent Application No. EP 0754437. This generator provides for different modes of operation, a first mode being a tissue desiccation or coagulation mode in which the peak voltage applied between the electrodes is limited to prevent vapour pocket formation at the tissue treatment electrode, and a second mode in which tissue is vaporised to produce a cutting or bulk removal effect at an operation site. During the second mode, the power supplied to the electrode assembly causes the formation, from the conductive liquid, of a vapour pocket around the tissue treatment electrode. In this case, the peak voltage applied to the electrode is limited to control the size of the vapour pocket and to prevent electrode destruction. A third mode of operation is a blended mode achieved by switching between the electrical conditions for the first and second modes.
The full subject matter of the above-mentioned applications is incorporated in this specification by reference.
Such an electrode assembly is typically introduced into body cavity through the working channel of an endoscope inserted through a natural body orifice or through a separate aperture formed to obtain access to the cavity. In either circumstance, the tubular instrument shaft provides the return path for electrosurgical currents, connection to the tissue treatment electrode being made through an insulated conductor passing through the shaft interior. The tubular member also provides for heat transfer away from the electrodes during operations. Thermal dissipation from the electrodes is enhanced by a portion of the shaft being immersed in the conductive liquid.
Endoscopic electrosurgery is useful for treating tissue in cavities of the body, and is normally performed in the presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery, this term denoting electrosurgery in which living tissue is treated using an electrosurgical instrument with a treatment electrode or electrodes immersed in liquid at the operation site. A gaseous medium is commonly employed when endoscopic surgery is performed in a distensible body cavity of larger potential volume in which a liquid medium would be unsuitable, as is often the case in laparoscopic or gastroenterological surgery.
Underwater surgery is commonly performed using endoscopic techniques, in which the endoscope itself may provide a conduit (commonly referred to as a working channel) for the passage of an electrode. A resectoscope is an endoscope specifically adapted to include means for mounting an electrode.
Endoscopic urological surgery is performed routinely to treat pathologies of the urinary tract, using a range of sophisticated instruments introduced through the urethra. Resectoscopes are a specific form of endoscope originally developed for urological surgery. They have since been used in hysteroscopic and gastrointestinal surgery for removal of soft tissues. Resectoscopes differ from many other endoscopes in that they include an integral trigger mechanism to produce a controlled forwards and backwards motion of an instrument attached to the mechanism. This control is particularly useful during removal of large volumes of tissue. As such, it is the instrument of choice for performing transurethral prostatectomy (TURP), the removal of a benign overgrowth of the prostate gland, endometrial and fibroid resection during hysteroscopic surgery, and the resection of polyps and tumours in the rectum during endoscopic gastrointestinal surgery.
Irrigating solutions may be delivered by continuous or intermittent flow through the resectoscope, and may be electrolyte or non-electrolyte based. As the traditional technique for performing TURP is monopolar electrosurgery, a non-electrolyte is most commonly used. Conventional instruments, therefore, comprise a range of monopolar electrodes mounted on the resectoscope.
Current resectoscopes are designed for use with monopolar electrodes. Essentially, this form of electrosurgery uses an electrode to supply current to the operating site, and to a patient earth plate to complete the circuit. Since the body is earthed, the procedure is carried out in a non-conductive fluid medium that prevents arcing away from the operative site.
As shown in FIG. 1, the known type of resectoscope consists of four main components, an inner sheath 1, an outer sheath 2, a rod lens telescope/light source assembly 3, a working element, indicated generally by the reference W, to the right of the dotted line shown in FIG. 1, and a monopolar electrode (not shown).
The sheaths 1 and 2 provide for the supply and aspiration of an operating site with a fluid medium via a connector 3a. The outer sheath 2 locks over the inner sheath 1, forming a watertight seal. Typically, the inner sheath 1 has a diameter of 24Fr, and the outer sheath 2 has a diameter of 27 Fr. The telescope assembly 3 provides the means of illuminating and viewing the operative site via a light source (not shown) connected thereto by a connector 4. The viewing angle of the telescope is generally at 30.degree. to its axis.
The working element W may be either passive or active, that is to say the cutting stroke of the electrode may be as the result of a spring bias or against the force of a spring bias. The telescope assembly 3 includes a telescope support tube, T having a telescope connector 5 at its proximal end, and a sealing block 6 located part way there along, the inner sheath 1 being connected to the sealing block. Both of these interfaces are watertight. An electrode support tube 7 is attached to the underside of the telescope support tube T on the distal side of the sealing block 6 for the majority of its length. Two spring-loaded links 8 and an insulation block 9, located between the sealing block 6 and the telescope connector 5, make up the mechanism. The active mechanism is arranged so that the spring-loaded links 8 assist the forward stroke, while, in the passive version the links aid the backward stroke. In general, the range of travel is about 25 mm.
The sealing block 6 has a hole through it to allow the telescope support tube T to be passed from the proximal to the distal end of the working element W, within the bore of the inner sheath 1. This hole is offset, so that the telescope is located in the upper quadrate of the inner sheath aperture to make room for the electrode support tube 7.
The monopolar electrode can be inserted down the electrode support tube 7 from the distal end thereof, and through a second hole in the sealing block 6. This hole is angled, so that the electrode exits the sealing block 6 at an increased distance from the telescope support tube T. This is necessary so the electrode can pass into the insulation block 9 with sufficient insulating material (.gtoreq.1.0 mm) being present between the electrode and the telescope support T to provide electrical isolation.
The need to bend the electrode shaft through the sealing block 6 inevitably increases the level of friction, and requires that the electrode shaft is very flexible. In addition, the diameter of that part of the electrode shaft which passes through the sealing block 6 is restricted to a maximum size of 2 mm.
The electrode is made watertight by a seal located in the sealing block 6. This seal is subject to wear, and is easily damaged. To compensate for this, an adjustment feature deforms the seal to maintain performance. Adjustment is not, however, possible when an electrode is fitted, so can only be carried out between procedures. The seals are prone to leak, and are generally replaced when the leakage becomes excessive.
The insulation block 9 contains a mechanism that grips the electrode shaft. While providing mechanical retention of the electrode, the mechanism is also the electrical connection to an electrical supply lead (not shown) via a connection socket 10 located on top of the insulation block 9. The block body is made of a non-conductive material to isolate the electrical path from the other parts of the resectoscope. PTFE is generally used, because it offers very low resistance to sliding.
This type of resectoscope has only been a practical proposition for monopolar electrode configurations. This is because the insulation block is of limited size, and would need to support two electrical conductors for a bipolar assembly, and these conductors would need to be spaced sufficiently apart from one another (and from the telescope tube) to ensure good electrical isolation. In practice, this is not possible with the known type of resectoscope, because both conductors must pass through a 2 mm aperture at the proximal end of the electrode support tube 7.
The difficulties of loading a bipolar electrode assembly into a resectoscope in the accepted way centre on the need to ensure electrical isolation within the insulation block. Whilst sufficient creep and air clearances can be achieved, the possibility of conductive fluid penetrating the block and causing a short circuit exists. This can occur during use if the shaft seal leaks, or during drainage of irrigation solution from a body cavity.